Environmentally associated colour divergence does not coincide with population structure across Lesser Antillean anoles

Abstract

Species distributed across heterogeneous environments may undergo local adaptation, which can be limited by the homogenizing effects of gene flow. Lesser Antillean anoles exhibit dorsal colour variation associated with dramatic shifts in environment across small spatial scales, providing an excellent system for studying the maintenance of local adaptation despite ongoing gene flow. The 1995 Soufriere Hills eruption on Montserrat provides an opportunity to understand how natural disasters may influence the evolution of insular species. Thus, our study had two main objectives. First, we collected genetic, phenotypic, and environmental data to investigate whether environmentally associated dorsal coloration reflects underlying population structure in three species of Lesser Antillean anoles. Second, we examined the short-term evolutionary consequences of volcanism by comparing pre- and posteruption samples of Anolis lividus using multilocus sequence data. We found all three species exhibited genetic isolation-by-distance but not isolation-by-environment. Furthermore, phenotypic differences within each species were not predicted by genetic distances, suggesting gene flow across colour morphs. We confirmed the repopulation of A. lividus in the impacted area and found genetic diversity equivalent to pre-eruption sampling. Our findings contribute to our understanding of local adaptation in spatially small-scale systems and the impact of catastrophic natural disasters on population structure.